Joule Thief

[resonanceman]

Joule Thiefe flash light with air core for a "used" AAA-battery

I post something very simple and down to earth (nothing special for a change). It is a Joule Thief circuit with an air core (instead of a toroid). The air core allows a high frequency of about 1 MHz.

About every 15 months I get 30 "used" AAA-batteries from my house alarm system. The batteries still show about 0.9 to 1.1 Volt when they are rejected as "low battery" by the window and door sensors.

The "flash light" was designed specially for those "used" batteries and gives many hours of light with a single "used" AAA-battery. When the battery gets weaker a jumper can be set to light fewer than 5 white LEDs.

I admit that one does not need such a flash light very often but it was fun to build it.

Greetings, Conrad

Conrad

Thats a great little project



The way  you chose to allow for a different  number of LEDs is great.

My only suggestion   would be to see if you can make it smaller.
You might  try a coil  with the same number of turns but without the tube. ..... If I was doing it I would  use the last  foot or 2 of wire and  go  around the loose wraps a dozen or so times to hold  everything together.
If it does not work  try again with longer  wire.
Same thing  with if you want higher  voltage........ longer  wire will help up to a point......after that it stops working.
I find most of my air cores need at least 5 ft of  wire for the base side of the primary...... 5 or more ft should  work for the emiter side......usually I use 3 to 5 times as much for that side.........for higher voltage.


gary

[conradelektro]

You might  try a coil  with the same number of turns but without the tube. ..... If I was doing it I would  use the last  foot or 2 of wire and  go  around the loose wraps a dozen or so times to hold  everything together.
If it does not work  try again with longer  wire.

gary

@ Gary (resonanceman): I would like to ask you to explain your suggestion (see the above quote) in other words or with a drawing. It sounds very interesting but I do not understand it (may be because I am not an English speaker).


@ all the nice commenters: the design of the flash light is awkward and the thing is clumsy, one could do much better with a little care and diligence. It is more an experiment than a practical device. Let's call it a retro-flash-light from the Frankenstein era.


I found that a slowly diminishing battery poses a problem when designing a Joule Thief type circuit

My design idea was a secondary and the jumper to light 1 to 5 LEDs according to the remaining power and voltage in a slowly draining AAA battery.

There is huge difference between a JT that gets 1.5 Volt or one that should run on 0.6 Volt. With 1.5 Volt a lot is possible, up to lighting neons or fluorescent lights. But below 1 Volt the world becomes small, because not only the voltage is low but also the amperage that can be drawn from the slowly dying battery has diminished.

Air cores: I always succeed to get high frequencies with air cores (between 100 KHz and several MHz) and I achieve only low frequencies with toroids (6 KHz to 15 KHz).

Secondary winding: for a very low power and low voltage JT (e.g. 0.6 Volt, 0.3 mA, low power red LED) one should not use a secondary. But once sufficient power (at least 20 mA) and enough voltage (at least 1.2 Volt) are available one should use a secondary and the result will be a nice high voltage on the secondary to light many LEDs.


Another idea (see drawing): as long as two AAA batteries are still fairly strong (down to 0.9 Volt) one uses two AAA batteries in parallel, but once the voltage drops below 0.9 Volt, one switches the two AAA batteries to a series connection (with a toggle switch, not automatically).

Greetings, Conrad

[nievesoliveras]

Maybe toggling is the same as swapping.

Check this last year's Composition of a battery swapper.
Both circuits are the same. They change the run battery and the charge battery positions.

Switch to one side uses one battery as runner and the other as charger then they are swapped around.

It was not my idea, I just composed it with somebody elses idea.

Jesus

[conradelektro]

@ Jesus (nievesoliveras):

Thank you for posting the charger circuits, I will try them one day.

Really strange way of switching the transistor and I do not see right away how the second battery can be charged without a diode.

Did you do experiments with this circuit?

Greetings, Conrad

[The Observer]

Greetings,

With the posting of the battery swapper I thought it may be relevant to post a new finding of mine.
(I'm sure others have figured this out, I saw something about it somewhere here..)

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I lost my Old Walkman a couple weeks ago that contained my 2 AA Rechargeable batteries (1.2 V Energizers).

   I have a cheap $1 store radio as backup that needs 2  AAA batteries... but I only had dead ones.

       I stuck 2 dead regular 1.5 V AAA batteries in the Energizer Battery recharger.

           They charged to 1.9 Volts (drop to 1.7 V after rest) ! And work fine for the day.

                  Long story short... after about 5 recharges... I think they are holding more and more charge.
                                       and are reacting equally despite the fact that one was originally .4 V and the other .9 V.
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They also appear to charge 'pell mell' and do not get significantly warm.

I have tried numerous battery charging/swap experiments with the Joule Thief and my Resonating Audio Transformer setup...
But they were with NiMh 1.2 V batteries.
One has to wonder what would happen with regular batteries now.

I thought I saw it mentioned that they need to be 'trained' a bit.
Meaning.. they need to be charged a few times before they start to work right.
This may be true.

Best Regards,
                    The Observer